Method of preparing difluorodiazine



Nov. 5, 1963 INFRARED ABSORPTION SPECTRUM WAVE NUMBERS IN CM- E. A. LAWTON ETAL 3,109,711

METHOD 0F PREPARING DIFLUORODIAZINE Filed June 15. 1960 O O s O O O) (D Z 0 II w 9 2 g m N O O 3 n BONVLLIWSNVHJ. maoaad INVENTORS DONALD PILIPOVICH EMIL A. LAWTON BY 1 MWZ-W ATTORN EY United States Patent Oflice 3,109,711 Patented Nov. 5, 1963 3,109,711 METHOD OF PREPARING DIFLUORODIAZINE Emil A. Lawton, Woodland Hills, and Donald Pilipovich,

Chatsworth, Calif assignors to North American Aviation, Inc.

Filed June 15, 1969, Ser. No. 36,327 14 Claims. (Cl. 23--205) This invention relates to a method of preparing difluorodiazine. More particularly, this method relates to a method of preparing difluorodiazine employing difluoroamine as one of the reactants.

Difluorodiazine has heretofore been prepared by two methods. In one of these methods, fluorine was reacted with hydrazoic acid to give fluorine azide. The fluorine azide so formed was then decomposed to give difluorodiazine. Hydrazoic acid is a highly explosive and toxic compound and fluorine azide is a highly explosive compound. Actual explosions are encountered in production of the latter. The other method consists of obtaining difluorodiazine as a gaseous by-product from the electrolysis of a melt of ammonium bifluoride. The chief product from the electrolysis is nitrogen trifluoride. The difiuorodiazine has been reported to be present in amounts as high as 24 weight percent, however, it generally is found to be present in amounts ranging from about 5 to about weight percent. A disadvantage of the electrolysis process is the difficulty of separation of the difluorodiazine from the nitrogen trifluoride. It is thus seen that need exists for an improved process for the preparation of difluorodiazme.

It is, therefore, an object of this invention to provide a process for the preparation of difluorodiazine. -It is also an object of this invention to provide a process of which difluorodiazine will be the chief product. Another object is to provide a relatively less hazardous process for the preparation of difluorodiazine than that which has been available in the prior art. A further object of this inven tion is to provide a process for producing difluorodiazine in high yields. Still other objects of this invention will be apparent from the disclosure which follows.

The above and other objects of this invention are provided by a method of preparing difluorodiazine comprising contacting (1) an alkali metal fluoride with (2) difluoramine, whereby (1) and (2) react and form difluorodiazine. A non-limiting example is the reaction between potassium fluoride and difluoramine to produce difluorodiazine. It is believed that the reaction is represented by the following equation wherein M represents an alkali metal atom. This equation, however, is merely postulated as an explanation of how the difluorodiazine is obtained and is not to be interpreted as a limitation of the method herein described.

The alkali metal of the alkali metal fluoride that is employed is any of the alkali metals of group I-A of the periodic table of elements, as found in the Handbook of Chemistry and Physics, 41st edition, published by the Chemical Rubber Publishing Co., Cleveland, Ohio. Sodium fluoride, potassium fluoride, rubidium fluoride, and cesium fluoride are used in the process with increased reactivity as the atomic weight of the alkali metal is increased in the order LiF NaF KF RbF CsR The difference in the reactivity of the alkali metal fluoride toward difluoramine may be due to the stability of an intermediate complex, namely, MF-HNF A method for the preparation of difluoramine is given in an article by E. A. Lawton and John Q. Weber in J.

Am. Chem. Soc., 81, 4755 (1959). In general, difluoramine and alkali metal fluorides react upon contact to produce difluorodiazine at temperatures as low as 58 C.

For example, difluoramine reacts readily with sodium fluoride at a temperature of 78 C., as well as at temperatures below this. In the case of potassium fluoride, a reaction was observed at a temperature as low as -45 C. to form the product difluorodiazine. The reaction of difluoramine with rubidium fluoride is still faster and proceeds rapidly at a temperature of -58 C. When cesium fluoride is used, the reaction with difluoramine is very rapid at temperatures of as low as -80 C. Thus, it is seen that the reaction can be carried out at a temperature as low as 80 C.

The alkali metal fluoride is usually employed in particle form of a size which will pass through from about an 8 to about a 200 mesh screen.

In order that the reaction proceeds at a measurable or favorable rate, it is preferred that the partial pressure of difluoramine !be relatively high compared to the partial pressure of other gaseous components, such as nitrogen and/ or oxygen, and/or other contaminants. Consequently, it is preferred to first place the alkali metal fluoride in the reaction vessel and then reduce the pressure of gaseous components by forming at least a partial vacuum in the vessel before admitting difluoramine.

It is found that an intermediate in the reaction is the formation of alkali metal fluoride-difluoramine complex which has the general formula MF-HNF wherein M is an alkali metal as defined above. The formation of this complex is aided when the difluoramine is in liquid form. Therefore, a preferred embodiment of this invention is to contact the alkali metal fluoride with difluoramine in liquid form. Although difluorodiazine is formed at the temperature at which difluoramine is in the liquid state, namely, -23.6 C., and lower, it is found that the reac tion proceeds at a much faster rate upon warming to above this temperature. Consequently, a, preferred embodimerit of this invention is to contact the alkali metal fluoride with difluoramine in liquid formand. then heat the mixture until difluorodiazine is evolved. Alternatively, the alkali metal fluoride is contacted with gaseous difluoramine and the reaction vessel then cooled, causing the difluoramine to liquefy and condense on the surface of the alkali metal particles. Thereafter, the mixture is again heated until difluorodiazine is evolved. Where the gaseous d-ifluorodi azine product is contaminated with other components, the product stream is passed through a cold trap maintained at a temperature of, say, -l42 C. in order to condense the contaminants. The difluorodiazine is collected and stored in glass or passivated stainless steel containers. Difluorodiazine finds use as a catalyst, as described by C. B. Colburn et al., J. Am. Chem. Soc., 81, 1697 (1959). It catalyzes the polymerization of methylmethacrylate, styrene, and cyclopentadiene at room temperatures. The polymerization of still other polymeric substances is catalyzed by difluorodiazine at higher temperatures.

The following examples will more clearly illustrate the process of this invention.

EXAMPLE I To a reaction vessel equipped with gas inlet and outlet means, means for maintaining a vacuum therein, heating and cooling means, and temperature and pressure indicating means, was added one part of potassium fluoride in particle form, wherein the particles were of a size which would pass through screens varying in size from about 8 to about 200 mesh. The reaction vessel was evacuated to a pressure of substantially 10* millimeters of mercury. An amount of difluoramine equivalent to 0.033 rnol per mole of potassium fluoride added was admitted to the reaction vessel. The temperature of the reaction vessel was maintained within the range of 10 C.-18 C. for a period of substantially 19.5 hours. The gaseous components were then withdrawn from the reaction vessel, passed through a cold trap maintained at substantially -142 C. and collected in a receiving vessel maintained at the temperature of liquid nitrogen. The contents of the trap maintained at -l42 C. were analyzed and found to be difluoramine equivalent to 14 percent of the total amount introduced into the reaction vessel. The component collected at the temperature of liquid nitrogen in liquid form was gasified and the gas analyzed. The latter gas was found to consist of a mixture of two isomers of difluorodiazine in 91 percent yield, based on the difference between the amount of difluoramine admitted to the reac tion vessel and the difluoramine condensed in the cold trap at l42 C. An infrared spectrum of the difluorodiazine is shown in the drawing. The various absorption peaks of the spectrum in the drawing are substantially the same as those reported in the J. Am. Chem. Soc., 81, 6397 (1959). A portion of the mixture of isomers of difluorodiazine prepared in Example I was chromatographed. The mass spectrum of this isomer is given in the following table:

Table I MASS SPECTRUM OF DIFLUORODIAZINE LOW BOILING ISOMER Pattern Pattern m/e Ion coctfieient coefficient literature b Mass/unit charge ratio. b Values of the pattern coeflicient taken trom the J. Am. Chem. Soc. article, supra.

v div/u.

The mass spectrum of the high boiling isomer was obtained by diflerence of the low boiling isomer from the table for the mixture and is given in the following table:

Table II I Mass/unit charge ratio. b The literature reference is the same as for Table I. div u.

The difluorodiazine contains substantially 42 weight percent nitrogen and 5 8 weight percent fluorine correspond ing to the formula N F EXAMPLE II The process of Example I was repeated with the modification that the difluoramine was maintained in contact with potassium fluoride for a period of 2% hours. In this time, 75% of the difluoramine was used up to form difluorodiazine in 82% yield.

2 EXAMPLE III The process of Example I was repeated with the modification that the potassium fluoride containing vessel was cooled with a Dry Ice-trichloroethylene bath and the difluoroamine partially condensed in the vessel. The reaction vessel was then warmed. to ambient temperature of substantially 20 C. Substantially all of the difluoramine admitted to the reaction was converted to difluorodiazine.

EXAMPLE IV The process of Example II was repeated with the modification that rubidium fluoride was substituted for the potassium fluoride. Thirty-five percent of the difluoramine was converted in an 84% yield to difiuorod-iazine in a period of substantially 1.5 hours and at a temperature of substantially 20 C.

EXAMPLE V The process of Example II was repeated with the modification that cesium fluoride was substituted for potassium fluoride. In a period of 35 minutes, at substantially 25 C., 26.5% of difluoramine was used up producing difluorodiazine in 84% yield.

EXAMPLE VI To the apparatus described -in Example I was added one part powdered potassium fluoride of a 150400 mesh particle size. The reaction vessel was heated to a tempera ture of substantially 150 C. over a period of about 2 hours and all the gases given off from the potassium fluoride were pumped out. The reaction vessel containing the potassium fluoride was then cooled to a temperature of substantially C. with a Dry Ice bath. An amount of difluoramine equivalent to about 0.1 mol per mol of potassium fluoride in the vessel was then added. The difluoramine was kept in contact with. the potassium fluoride until equilibrium was reached as indicated by no further change in the pressure. The pressure was then recorded. The equilibrium point was approached from both directions, by cooling, and by upsetting the equilibrium through removal of HNF The equilibrium vapor pressure at different temperatures is recorded in the following table:

Table III DISSOCIA'IION PREssUREs OF KF-HNF:

Run I Run II T C Pmm T C. Pmm

The variation of the dissociation pressure with temperatures is given by the following equation:

wherein T is given in degrees absolute. the heat of the reaction for From the slope,

was calculated to be 6.7 kcaL/mole. The dissociation pressure is one atmosphere at about 26 C. by extrapolation. Since the vapor pressure of difluoramine at -81 C. is substantially 22 mm.., the observed vapor pressure of 1.5 mm. as given in Table III can only be explained by complex formation. A complex formation is indicated in which the difluoramine is bonded to the potassium fluoride by a hydrogen bond. In the same manner, the formation of RbF-HNF complex and CSF-HNF complex were shown.

Both rubidium fluoride and cesium fluoride react with difluoramine at room temperature, the latter at times explosively, especially if foreign matter is present.

EXAMPLE vn A cylindrical reaction vessel was equipped with gas inlet and outlet means, and means for introducing solid material. The vessel was also equipped with means for evacuating and maintaining a vacuum, as well as means for conducting a gas therethrough in a controlled manner so as to provide for a specified residence time within the reaction vessel. Means were also provided for passing product gases emerging from the vessel through a system of cold traps for separation of the components. The reaction vessel was packed with rubidium fluoride of a particle size which will pass through a 120 mesh screen. The vessel and contents were placed in a tube furnace and evacuated while heating to a temperature of about 90 C. After evacuation, the temperature of the reaction vessel and the rubidium fluoride was adjusted to 81.5 C. An amount of difluoramine, much less than the stoichiometric value required to react with the rubidium fluoride present according to the equation given hereinaJ-bove, was conducted through the reaction vessel at a rate which would provide a residence time of substantially 9 minutes. The gases emerging from the reaction vessel were conducted through two cold traps, one maintained at l42 C. and the second maintained at --196 C. All components except the product difluorodiazine were condensed in the first cold trap and the difluorodiazine collected in the second cold trap. An analysis of the first cold trap showed that 43% of the difluoramine had reacted. A quantitative analysis of the difluorodiazine collected in the second cold trap showed that the product had formed in a 53% yield, based on the difluoramine used up.

EXAMPLE VIII The procedure of Example VII was repeated with the modification that the reaction vessel was maintained at 121 C. while passing the difluoramine therethrough. It was found that 87% of the difluorasmine passed through the reaction vessel was converted to difluorodiazine in 100% yield. The residence time within the reaction vessel was 9 minutes.

EXAMPLE IX The procedure of Example VII is repeated with the modification that the temperature of the reaction vessel is maintained at substantially 225 C. and the residence time is substantially one second. A good yield of difluorodiazine is obtained.

EXAMPLE X The procedure of Example VII is repeated with the modification that the temperature of the reaction vessel is maintained at substantially 25 C. and the residence time is substantially minutes. A good yield of difluor-odiazine is obtained.

EXAMPLE XI The procedure of Example VII is followed employing potassium fluoride as the solid component while maintaining the reaction vessel at a temperature of substantially 250 C. The difluoramine is passed through at a rate such as to provide a residence time of substantially one minute. A good yield of difluorodiazine is obtained.

EXAMPLE XII The procedure of Example XI is repeated with the modification that the reaction vessel is maintained at a temperature of substantially C. and the residence time is substantially 25 minutes. A good yield of difluorodiazine is obtained.

EXAMPLE XIII The procedure of Example VII is repeated employing cesium fluoride as the solid component. The reaction 6 vessel is maintained at a temperature of substantially C. The difluoramine is passed through the reaction vessel at a rate such as to provide for a residence time of substantially 0.1 second. A high yield of difluorodiazine is obtained.

EXAMPLE XIV The procedure of Example XIII is repeated with the modification that the temperature of the reaction vessel is maintained at substantially 25 C. and the residence time is substantially 5 minutes. A good yield of difluorodiazine is obtained.

The use of a flow system in carrying out the reaction forms another preferred embodiment of this invention. From Examples VII-XIV above, it is seen that high yields of difluorodiazine are obtained when difluoramine in gaseous form is passed through a bed of an alkali metal fluoride. The examples illustrate that reactions occur within the temperature range of from about 25 C. to about 225 C. at residence times of from about 0.1 second to about 25 minutes. Temperatures below about 25 C. can be employed but the reaction at the lower temperatures is slowed down. On the other hand, a reaction zone temperature of about 225 C. provides a fairly rapid rate of reaction and there is, therefore, no great advantage gained in going to higher temperatures.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. A method of preparing difluorodiazine comprising contacting the reactants (1) an alkali metal fluoride with (2) difluoramine, whereby (1) and (2) react and form difluorodiazine.

2. The method of claim 1, with the additional step of separating said difluorodiazine from unreacted difluoramine.

3. A method of preparing difluorodiazine comprising contacting (1) an alkali metal fluoride with (2) difluoramine in the liquid state, where (1) and (2) react and difluorodiazine is produced.

4. The method of claim 3, wherein said alkali metal fluoride is potassium fluoride.

5. A method of preparing difluorodiazine comprising contacting (1) an alkali metal fluoride with (2) difluoramine in the liquid state, whereby (1) and (2) react and difluoraodiazine is produced to form a mixture of 1) and (2) and difluorodiazine, heating said mixture and removing said difluorodiazine product.

6. The method of claim 5, wherein said alkali metal fluoride is potassium fluoride.

7. A method of preparing difluorodiazine comprising contacting (1) an alkali metal fluoride with (2) gaseous difluoramine, cooling said (1) and (2) down to at least the condensation point of said diflluoramine, whereby said difluoramine is condensed on said alkali metal fluoride, whereby said (1) and (2) react and form difluorodiazine.

8. The method of claim 7, wherein said alkali metal fluoride is potassium fluoride.

9. A method of preparing difluorodiazine comprising contacting (1) an alkali metal fluoride with (2) gaseous difluoramine, cooling said (1) and (2) down to at least the condensation temperature of difluoramine, whereby a mixture of solid alkali metal fluoride and liquid components is formed, thereafter heating said mixture to reach the boiling point of the liquid therein, whereby difluorodiazine is formed by the reaction of said alkali metal fluoride in contact with said difluoramine.

10. The method of claim 6, with the additional step of separating said difluorodiazine from unreacted difluoramine.

I 8 11. A method of preparing difiuorodiazine compris- 14. The process of claim 12, wherein said alkali metal ing contacting (1) potassium fluoride with (2) difluorafluoride is rubidium fluoride.

mine, whereby (1) and (2) react and difluorodiazine References Cited in the file of this patent is produced.

12. A process for the preparation of difluorodiazine 5 UNITED STATES PATENTS comprising passing difluoramine through a bed of an 2,958,634 Cleaver Nov. 1, 1960 alkali metal fluoride, whereby difluorodiazine is formed.

13. The process of claim 12, with the additional step OTHER REFERENCES t of separating the product difiuorodiazine from unreacted snefid 6t cmnprfihenslve Inorganic y,

difluoramine. 10 D. Van Nostrand and Co., Inc., N.Y., vol. 5, page 81.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION @Patent No. 3 109311 November 5, 1963 Emil A. Lawton et alq It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 Table l, fourth column, line 4 thereof for '50 read 5.0 same column, line 45, before "ISOMER" insert BOILING column 4, line 63, for "6.7 kcal./mo1e" read 6.7 k. caln/mole line 72 for "CSF HNF read CSF'HNF2 column 6, line 43, for "where" read whereby Signed and sealed this 16th day of June 1964.

#SEAL) ttest:

RNEST W. SWIDER EDWARD J. BRENNER (testing Officer Commissioner of Patents 

1. A METHOD OF PREPARING DIFLUORODIAZINE COMPRISING CONTACTING THE REACTANTS (1) AN ALKALI METAL FLUORIDE WITH (2) DIFLUORAMINE, WHEREBY (1) AND (2) REACT AND FORM DIFLUORODIAZINE. 